Carbon overcoat: Structure and bonding of Z-DOL

Thin carbon films (similar to 10 nm) sputter-deposited on silicon wafers fr om a graphite target were examined by ESR (electron spin resonance) spectro scopy, and atomic force microscopy. The study revealed that such carbon fil ms are best described as a stack of closely packed spheroidal granules with diameters of several nanometers, with the actual dimension depending on th e sputtering condition. The atomic bonding scheme within each individual gr anule would be either the sp2 type (graphitic) or the sp3 type (diamond lik e). The granules of the sp3 type host the dangling bonds responsible for th e ESR signal. Each spheroid of the sp3 type thus comprises a mantle and a c ore; the mantle layer is formed when freshly prepared film is exposed to am bient atmosphere and labile molecules (e.g., oxygen or water) diffuse into the spheroid and react with dangling bonds. The mantle layer thus formed be comes a protective shield for the dangling bonds remaining in the core. The density of dangling bonds within the core may be as high as 1 per 100 carb on atoms. When sputter-deposited films were left in an intimate contact wit h molecules with hydroxyl groups (e.g., water or Z-DOL), an irreversible re action occurred involving dangling bonds. The reaction is ascribed to a hyd rogen atom transfer from the hydroxyl group to a dangling bond in the core and is postulated to be the mechanism of the Z-DOL bonding. The atomic forc e microscopy examination revealed surface features that were consistent wit h the stacked spheroid model. The spheroid diameter inferred from the [roug hness](rms) measurement is in good accord with the dimension estimated from the ESR study.